Logic

loj'ik, the art of reasoning. Logic enables the student to distinguish between true and false argument. There are many forms of reasoning. One of the simplest is the following:

Such a form is called a syllogism. The first statement is called the major premise; the second, the minor premise; the third, the conclusion. If the premises be true, the conclusion must be true. This sort of reasoning is employed largely in geometry, as:

In argument of this sort, liability to error lies chiefly in assuming a false major premise. In the days preceding the American Revolution the British authorities argued as follows:

The American colonists argued as follows:

So far as the form of argument is concerned, both syllogisms are correct. The different conclusions drawn are due to starting from contradictory major premises.

The early colonists of Virginia sent back their vessels to England loaded down with iron pyrites, or fool's gold. Thrown into a syllogism, their argument was as follows:

In their syllogisms, both premises are true, but the conclusion does not follow from the premises. It is not true. The metal was not gold.

In his unique poem of The Deacon's Masterpiece, or The Wonderful One-Hoss Shay, Dr. Holmes presents two syllogisms, the deacon's and his own. Both are fallacies. The reader may decide whether the fallacies lie in the premises or in the conclusions. The deacon's syllogism is as follows:

Holmes's syllogism is the following:

As may be remembered, he leaves the argument with "Logic is logic. That's all I say."

In syllogistic argument, we proceed from general statements to a definite one. From "All men are mortal," and "Enoch is a man," the syllogistic logician argues that "Enoch must die." This form of argument is called deduction. Turned end for end, the argument runs, "Enoch died, Columbus died, George Washington died, a million other men have died, hence all men die." In other words, man is mortal. This is called inductive reasoning.

The latter is the form employed usually by scientists. When a wheat buyer sends a man to draw a few ounces of wheat from different parts of a car and puts them together as a sample, he infers by inductive reasoning the kind and quality of wheat contained in the car. The more samples he has from the car, the more certain his conclusion. The directors of the United States census have observed that, for the past hundred years or more, the center of population has moved steadily westward from a point near the Atlantic coast to a point in 1900, near the city of Columbus, Indiana. We are justified by induction in concluding that the census of 1910 will locate the center still nearer Indianapolis.

This sort of reasoning is open to error. Although we may have seen half the beans in a bag, we cannot be certain that all the beans are sound until we have examined the last one. The more instances we observe, the more certain our conclusion. The early settlers of Minnesota had so many failures and disappointments that they jumped at the conclusion that corn and apples could not be raised in the state. Persistent efforts and a later trial of varieties better adapted to the climate have demonstrated that the logic of the pioneers was utterly at fault.

Far from being restricted to the college and the school, it may be said, as of no other subject, that logic, whether deductive or inductive, is but the application of shrewd common sense. Many of our popular sayings are logical conclusions of the shrewdest sort: